Pulsed photoconductivity in diamond upon quasi-continuous laser excitation at 222 nm at the formation of an electron-hole liquid

An order-of-magnitude enhancement of the pulsed photocurrent in a polycrystalline diamond sample synthesized by chemical vapor deposition is observed under the conditions of formation of an electron-hole liquid. Nonequilibrium charge carriers are excited by laser pulses at a wavelength of 222 nm with FWHM pulse duration of 18 ns and peak intensity above 2.5 MW/cm$^2$ upon cooling the sample to 90 K. For peak intensities of laser excitation lower than 1 MW/cm$^2$, sample cooling from 300 to 90 K leads to a decrease in pulsed photocurrent by about a factor of 5. The observed increase in pulsed photocurrent is attributed to the formation of the electron-hole liquid.